The present invention relates to printing presses and more particularly to a fountain for applying a foam ink to an engraved printing cylinder of a rotogravure printing press.
Rotogravure printing is typically done with hydrocarbon based liquid inks or water based liquid inks, which in most cases contain some volatile organic compounds as drying agents. Ink is applied to the engraved cylinder by one of the following methods: (a) immersing a portion of the cylinder in a bath of ink; (b) spraying ink onto the cylinder by means of nozzles; or (c) from a roller frictionally driven by contact with the cylinder, a portion of the roller being immersed in a bath of ink. All of these methods are designed to insure that the ink completely covers the surface of the cylinder and fills the engraved cells. In reality, however, all the systems may produce intermittent void areas known as "skips".
Another type of ink, water based foam, has proven to be an equivalent substitute for conventional hydrocarbon based rotogravure inks. But the foam ink has a relatively low mass and is adversely affected by air currents, so that the conventional bath is not suitable. This is because the laminar boundary layer of air on the surface of a rotating cylinder blows the ink away. A friction driven roller applicator squeezes the gas out of the foam breaking down the foam into a liquid, thus altering the characteristics of the foam ink so that it is unsuitable for printing. And appying foam ink through a plurality of nozzles in an attempt to avoid "skips" requires far more ink than the cylinder can accept.
The U.S. Pat. No. 4,365,968 discloses a method of treating textiles serially with two finishing agents, one or both of which are in the form of a foam. The second agent, which is always a foam, is applied before the textile has been fully dried after application of the first agent, which may be a printing composition.
The U.S. Pat. No. 4,266,976 discloses a similar method of treating textiles with foam finishing agents and describes various compositions suitable for fabrics, all of which must be stable for a relatively long period of time.
The U.S. Pat. No. 2,971,458 describes a process for coloring textiles using various foamed inks, the ink being applied to the engraved printing cylinder under pressure through an enclosed distributor box to prevent ambient air from contacting the foamed ink. Mention is made of a technique in which foam is applied to the printing cylinder by a cylindrical brush from a furnishing box, high speed beaters being provided in the box in an attempt to overcome the tendency for the air content of the foam to increase.
The U.S. Pat. No. 3,400,658 discloses a method of rotogravure printing in which a foam ink is injected and contained in a pressurized chamber in contact with the printing cylinder for a very short period of time, the chamber excluding ambient air from contact with the foam ink in the chamber. This system requires the ink to be continuously removed from the chamber to a remote compressor and recirculated to the chamber so that it is refoamed during each cycle.